She found that mutations to the gene CYP2A6, which previously had been linked to smoking behaviour and nicotine metabolism, is also linked to caffeine metabolism.

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Furthermore her team discovered that genetic variants linked to faster caffeine metabolism are the same ones responsible for encouraging higher coffee consumption.

Dr Cornelis said: “This makes sense, conceptually, but the genetic research confirms it and further re-emphasises the notion that not everyone responds to a single cup of coffee (or other caffeinated beverage) in the same way.”

The research also showed the genes which metabolise caffeine are also linked to the metabolism of other clinically important drugs, such as those that treat insomnia and Parkinson’s disease.